1. Field of the Invention
The present invention is generally related to communication systems and in particular to reliable transmission of signaling information in wireless communication systems.
2. Description of the Related Art
Communication systems and, in particular, wireless communication systems convey (i.e., transmit and/or receive) information in channel coded form over communication channels. The channel coding helps protect the integrity of the information being conveyed over communication channels of a communication system. In particular, the channel coding of the information is done to help detect any errors when the information is received after such information has propagated (in the form of a communication signals) over the communication channels of a system. The channel coding also serves the purpose of reducing the likelihood of errors occurring in the conveyed information where such errors are due to anomalies that exist in the communication channels. As such, the channel coding is not used only for error detection but also for error correction.
In a typical communication system, the information being conveyed between users of such systems, i.e., user information, is processed in accordance with various rules and protocols that are part of a standard typically established by a communication standards body. The user information is typically conveyed over data or traffic channels. In addition to user information, signaling information is conveyed between users and between equipment of the communication system to implement the particular protocol with which the communication system complies. Signaling information, which is conveyed over signaling or control channels, is generated by various equipment (user and/or system) of the communication system. The signaling information provides the rules by which user information is processed, transmitted and received by various equipment of the communication system. The signaling information represents and executes the protocol of the communication system.
Many communication systems comply with standards that require the use of more than one control channel per data channel. For example, in Code Division Multiple Access (CDMA) communication systems that comply with the cdma2000-1x-EV-DV standard, there are two control channels per data channel. The control channels associated with a data channel carry signaling information that dictate how the user information is transmitted over the data channel and how the user information is processed after having propagated through the data channel. The first control channel, which is called the primary control channel, contains timing information for the user information. The second control channel, which is called the secondary control channel, contains various information that describe the format and the identification of the user information being transmitted over the data channel.
In CDMA systems complying with the cdma2000-1x-EV-DV standard, information in both control and data channels are transmitted in the form of sub-packets during one or more time slots. The cdma2000-1x-EV-DV standard has defined a time slot to be 1.25 milliseconds in duration. At the transmit end, a block of user information—usually a group of bits—is coded and the resulting coded block of user information, which is called a packet, is divided into several sub-packets. The channel coding of the user information is done such that the information contained in the original block of user information can be retrieved from one or a combination of any number of the sub-packets. The amount of information contained in the original block is called the payload size. The payload size is part of the information included in the secondary control channel information.
The secondary control channel information, which is transmitted in parallel and in synchronization with the user information, also contains other information. In particular, the secondary control channel information includes the MAC ID of the sub-packet which identifies a user on a shared channel. The secondary channel information further includes: (1) the Sub-packet ID which identifies a particular sub-packet being transmitted over a data channel; (2) Automatic Retransmission reQuest (ARQ) channel ID which identifies a logical ARQ channel; (3) New packet indication which identifies the first sub-packet of a group of sub-packets being transmitted or acts to demarcate one group of sub-packets from another group.
The primary control channel contains information about the particular time slot or slots to which a sub-packet in a particular data channel is assigned. The primary control channel information not only dictates the number of slots used for the data channel but also indicates the number of slots used for the secondary control channel. For example, a primary control channel contains information indicating that the secondary and data channels will be transmitted during four time slots. Consequently, the sub-packets associated with the secondary channel and data channels are transmitted during four time slots. Therefore, if the primary control channel is received with errors, the information contained in the secondary channel and the data channel will not be decoded properly. Continuing with the example above, if a receiver receives erroneous primary control channel information indicating that the secondary channel information and the data channel information are to be transmitted during three time slots, the receiver will attempt to decode only three time slots worth of secondary control channel information and three time slots worth of data channel information. In some cases, the secondary channel information may still be correctly decoded because they are repeated in each slot. However, in most cases the received information (user information and secondary control channel information) will be improperly decoded and improperly retrieved resulting in errors. Therefore, there is some uncertainty in the ability to correctly decode the secondary control channel and data channel information because of lack of reliability in the primary control channel information. In other words, the proper decoding of secondary channel information does not necessarily mean that the primary channel information was error free. Further, even if the secondary channel information is properly decoded from erroneous primary channel information, the data channel information may still be improperly decoded. The problem of erroneous signaling information is typically addressed by increasing the amount of channel coding applied to such information and to the user information.
The error detection and error correction codes added to the user and signaling information help to negate the effects of noise sources and other anomalies on the user and signaling information propagating through the data and control channels respectively. However, error correction and error detection coding typically require additional channel capacity because such coding cause more information to be conveyed in the signaling and user channels. Usually there is a direct relationship between capacity and transmission power requirements and a direct relationship between capacity and bandwidth requirements of a communication system. Service providers, which are entities that own, operate or otherwise control communication systems, thus have to bear the extra costs of additional capacity, power and bandwidth associated with the additional channel coding used for the communication channels of their communication system. In particular, the signaling channels typically require more robust channel coding than the data channels because the signaling information contain critical timing and processing information that are used to decode and retrieve the user information. User information cannot be properly decoded if associated signaling information is received in error; this is so regardless of whether the user information itself is received with or without errors. In communication systems such as cdma2000-1x-EV-DV compliant CDMA systems which have more than one signaling channel, the use of additional and more robust channel coding in the signaling channels has an even more burdensome effect on system resources such as transmission power, bandwidth requirements and capacity requirements.
What is therefore needed is a method of further protecting the integrity of signaling channel information without having to increase the amount of channel coding applied to such communication channels. In particular for cdma2000-1x-EV-DV compliant CDMA communication systems, what is further needed is a method where the errors occurring in the primary control channel can be detected and corrected without the use of additional channel coding thus allowing the received secondary control channel information and the received data channel information to be decoded correctly.